An interferometric measuring method, as well as a measuring device are described in the German Published Patent Application No. 198 08 273. In this conventional interferometric measuring method, based on the principle of heterodyne technology, an acousto-optical modulator is used to shift the light frequency having a heterodyne frequency to facilitate the evaluation, and the distance to or the shape of the surface is determined by evaluating the phase difference. In this context, the phase differences in light components of the light, which is obtained from a short-coherent light source, split by a beam splitter into different wavelength ranges, and detected by a photodetector array, are simultaneously evaluated on the basis of the particular phase difference. Upon consideration of the phase difference, in the context of light of only one wavelength, the range of unambiguity may be limited to a change in distance between two measuring points of less than one half of the corresponding wavelength. On the other hand, a synthetic wavelength Λ=λ1·λ2/(λ2−λ1) may be formed from at least two different wavelengths. From this follows a correspondingly larger unambiguity range, in which a correspondingly rougher measurement may be taken as a single-valued measurement. However, the increased unambiguity range may be associated with additional outlay.
U.S. Pat. No. 5,293,215 describes an interferometric measuring device which is likewise based on the concept of multi-wavelength heterodyne interferometry, wherein a frequency-modulated light-generating device having a plurality of frequency-modulated lasers as light sources for the various wavelengths is used.
U.S. Pat. No. 5,883,715 discusses an interferometer having a frequency-modulated light source for a vibrometer.